The consequences of postpartum depression (PPD) extend far beyond the mother's mental health, and can have severe detrimental effects on marital relationships, parenting abilities, mother-infant bonding, and infant health and development. Although Latinos are the fastest growing population group in the US, few studies of PPD have been conducted with Latina women. Existing studies suggest a significantly elevated vulnerability to PPD for low income ethnic minority women. However, the trajectories of onset and recovery have not been well- described, and little is known about the influence of cultural-ecological risk and protective factors. Further, most research has failed to consider the fundamental role of the newborn baby and the ability of mother-infant interactions to influence the onset and course of PPD. This study will evaluate a community sample of 330 low-income Mexican American first- time mothers from the prenatal period through the first postpartum year. The development of PPD and the process of recovery will be examined using well-validated symptom and clinically diagnostic measures. Culturally-ecological factors will be examined that may either confer risk or offer protection from PPD. Repeated home observations of mother-infant interactions will be collected in the critical first 6 months following childbirth. The bio-psychosocial process by which mothers and infants co-regulate each other's emotions, behavior, and physiology will be analyzed and used to predict the longitudinal course of PPD over the first year. Findings will significantly enhance understanding of the impact of culturally-relevant risk and protective factors on the onset and course of PPD in a highly vulnerable population, and will identify innovative targets (e.g., mother-infant interactions) for future interventions.